D. Chiumello
E. Gallazzi
A. Marino
V. Berto
C. Mietto
B. Cesana
L. Gattinoni
A validation study of a new nasogastric
polyfunctional catheter
Received: 4 August 2010
Accepted: 24 November 2010
© Copyright jointly held by Springer and
ESICM 2011
D. Chiumello and L. Gattinoni participated
in the development of Nutrivent, but do not
have any patent or financial agreement, and
received only an honorarium as members of
the advisory board.
D. Chiumello (✉) 4 V. Berto 4 C. Mietto 4
L. Gattinoni
Dipartimento di Anestesia, Rianimazione
(Intensiva e Subintensiva) e Terapia del
Dolore, Fondazione IRCCS Ca’ Granda,
Ospedale Maggiore Policlinico, Via
Francesco Sforza 35, 20122 Milan, Italy
e-mail: chiumello@libero.it
Tel.: ?39-02-55033237
Fax: ?39-02-55033230
E. Gallazzi 4 A. Marino
Dipartimento di Anestesiologia, Terapia
Intensiva e Scienze Dermatologiche,
Universita` degli Studi di Milano,
Milan, Italy
B. Cesana
Unita` di Statistica Medica e Biometria,
Dipartimento di Scienze Biomediche e
Biotecnologie, Universita` degli Studi di
Brescia, Brescia, Italy
Abstract Purpose: Pleural and
abdominal pressure are clinically
estimated by measuring the esopha-
geal and bladder or intragastric
pressure (IGP), respectively. A new
nasogastric polyfunctional catheter is
now commercially available, equip-
ped with two balloons in the lower
and distal part; this catheter allows
simultaneous esophageal pressure
(Pes) and IGP measurements and can
be also used to feed the patient. We
compared the Pes and IGP measured
using this new device with those
obtained with a standard balloon
catheter taken as gold standard.
Methods: Twenty-four intubated
patients requiring ventilator support
(mean age 64.3 ± 16.8 years, body
mass index 25.3 ± 3.0 kg/m2, and
PaO2/FiO2 280.8 ± 123.4 mmHg)
were enrolled. Esophageal pressure
and IGP were measured with the new
nasogastric polyfunctional catheter
(Nutrivent, Sidam, Italy) and with a
standard balloon catheter (Smart Cath
Viasys, USA). The Smart Cath was
first inserted in the stomach and then
retracted to the esophagus to measure
IGP and Pes, respectively. In each
patient two paired measurements
were averaged. Results: In the
Bland–Altman analysis, the bias and
agreement bands for Pes, DPes
(computed as the difference of
esophageal pressure between end-
inspiration and expiration), and IGP
were -0.25 (-2.65 to ?2.15), 0.0
(-0.9 to ?0.9), and -0.45 (-2.85
to ? 1.95) cmH2O, respectively. No
side effects or complications were
recorded. Conclusions: The new
polyfunctional catheter showed a
clinically acceptable validity in
recording esophageal and intragastric
pressure. This device should help
physicians to better individualize the
clinical patient management.
Keywords Nasogastric catheter 4
Esophageal pressure 4 Intragastric
pressure 4 ARDS
Introduction
Acute lung injury (ALI)/acute respiratory distress syn-
drome (ARDS) is a syndrome which, despite recent
therapeutic advances, still results in high mortality [1, 2].
Although mechanical ventilation is a life-saving support,
it may induce several types of lung injuries collectively
named as ventilator-induced lung injury (VILI) [3]. The
lung inflation depends on transpulmonary pressure (air-
way pressure minus pleural pressure), which in turn
depends on the characteristics of the chest wall and the
lung [4, 5]. In addition, an abnormal increase in the intra-
Intensive Care Med
DOI 10.1007/s00134-011-2178-4
ORIGINAL
abdominal pressure, defined as intra-abdominal hyper-
tension, is frequently reported (from 18 to 81%) in
critically ill patients [6, 7].
The absence of a customized lung protective strategy
based on the transpulmonary pressure could lead to an
under- or over-application of positive end-expiratory
pressure (PEEP) as well as misinterpretation of the airway
pressure [8]. The esophageal pressure measured in the
lower third of the esophagus is an adequate surrogate of
the pleural pressure, because the esophagus behaves as a
passive structure [9–11]. The intra-abdominal pressure
can be estimated by measuring the bladder or the intra-
gastric pressure [12].
There is currently no nasogastric catheter available
which allows a continuous and simultaneous monitoring
of the esophageal and intragastric pressure while also
providing the possibility of feeding the patient. The aim
of this study was to evaluate the accuracy of the esoph-
ageal and intragastric pressures measured with a new
nasogastric polyfunctional catheter compared to those
obtained by a standard balloon catheter.
Materials and methods
Subjects
Twenty-four intubated, mechanically ventilated, sedated
patients, with or without paralysis, admitted to our
intensive care unit (ICU) from January to June 2010 were
enrolled. Baseline characteristics were mean age
64.3 ± 16.8 years, body mass index 25.3 ± 3.0 kg/m2,
new simplified acute physiology (SAP) II score 39.3 ±
12.2, PEEP 6.3 ± 4.5 cmH2O, PaO2/FiO2 280.8 ± 123.3,
and tidal volume 492 ± 116 ml. Inclusion criterion was
the presence of mechanical ventilation in patients who
required a catheter. Exclusion criteria were patients
younger than 16 years, documented barotrauma, high
grade of esophageal varices, a recent history of esopha-
geal or gastric surgery, and severe coagulopathy. The
study was approved by the institutional review board of
our hospital, and informed consent was obtained accord-
ing to the Italian national regulations.
Measurement
Esophageal and intragastric pressure were simultaneously
recorded by using the new nasogastric polyfunctional
catheter (Nutrivent, Sidam, Mirandola, Italy) and by a
standard balloon catheter (Smart Cath, Viasys, Palm
Springs, USA).
The Nutrivent consists of a polyurethane tube (110-cm
long with an external diameter of 4.7 mm) with multiple
small holes and two thin-walled polyethylene balloons
(10-cm long and 15-mm diameter) incorporated in the
lower and in the distal portion of the tube (Fig. 1). The
intragastric position of the distal catheter was confirmed
by aspiration of gastric juice, auscultation of air insuf-
flations into the stomach, and by a rise in intra-abdominal
pressure following external manual epigastric pressure.
The balloon position in the lower third of the esophagus
was confirmed in patients with paralysis by concordant
positive changes in airway, esophageal and intragastric
pressures during an inspiratory occlusion [13], and in
patients able to perform an inspiratory effort by per-
forming the Baydur test [14].
For an optimal reading of the pressures, the balloon
should be inflated with an adequate volume of air so as to
transmit the pressure without artifacts. Previous in vitro
evaluation showed that the optimal volume both for the
esophageal and gastric balloons was 4 ml of air.
The Smart Cath consists of a tube 103 cm long with an
external diameter of 3 mm and a thin-walled balloon
(10 cm long) located in the distal part. To measure the
intragastric pressure, the catheter was first positioned in the
stomach at a depth of 45–55 cm and then inflated with a
volume of 2 ml of air. Subsequently, to measure the
esophageal pressure, the catheter was retracted until it
reached the upper third of the esophagus at a depth of 30–
35 cm from the mouth. The Smart Cath does not allow one
to aspirate the liquid from the stomach or to feed the patient.
Pressure signals were measured by pressure transducers
(Bentley Trantec; Bentley Laboratories, Irvine, USA) and
recorded on a personal computer for subsequent analysis
(Colligo, Elekton, Milan, Italy). Two-min recording
sections were performed. In each patient two paired mea-
surements were averaged for the analysis. The two
catheters were positioned at the same time in the patients
and the measurements were obtained at the same time.
Protocol
Patients were in the supine position on mechanical ven-
tilation with pre-study ventilator settings. The esophageal
Fig. 1 a Schematic drawing showing the technical characteristics
of the Nutrivent
pressure was measured during an end-inspiratory and an
end-expiratory occlusion of the airway (PesEIO and
PesEEO). The variation of esophageal pressure during tidal
inflation (DPes) was computed as PesEIO minus PesEEO.
The intragastric pressure was measured only during an
end-expiratory occlusion of the airway (IGPEEO).
Statistical analysis
Data are presented as mean ± standard deviation (SD). In
addition, 95% confidence intervals (CI) were reported
when necessary. Esophageal and intragastric pressures
measured with the new nasogastric polyfunctional cath-
eter and the standard balloon catheter were compared
according to Bland–Altman analysis [15] together with
the Passing and Bablok non-parametric regression [16]
and concordance correlation coefficient [17]. Statistical
analysis was performed with SAS(c) 9.1.
Results
Esophageal pressure
The mean PesEEO
and DPes were 12.8 ± 3.1 and
3.2 ± 1.4 cmH2O, respectively, for the new nasogastric
polyfunctional catheter and 12.9 ± 2.8 and 3.3 ± 1.5
cmH2O for the standard balloon catheter. The regression
equations, calculated according to the Passing and Bablok
method, had an intercept of -0.6909 (95% CI -3.1554 to
0.9022) and a slope of 1.0349 (95% CI 0.9130–1.2162)
for the PesEEO and an intercept of -0.1500 (95% CI
-0.6500 to 0.4071) and a slope of 1.000 (95% CI 0.8571–
1.2000) for DPes.
In the Bland–Altman analysis, the bias and agreement
bands (between brackets) for PesEEO (Fig. 2a) and DPes
(computed as the difference of esophageal pressure
between end-inspiration and expiration, Fig. 2b) were
-0.25 (-2.65 to ?2.15) and 0.0 (-0.9 to ?0.9) cmH2O,
respectively. There was no evidence of an increase of bias
at the extremes of the pressure range (p = 0.1936 and
0.3593, respectively). The concordance correlation coef-
ficient (CCC) was 0.91 (95% CI 0.80–0.96) for the PesEEO
and 0.95 (95% CI 0.90–0.98) for DPes; these values
translate into a within-sample variability of about 30%
and 22% of the total variability, respectively.
Intragastric pressure
The mean IGPEEO was 9.7 ± 2.7 and 10.2 ± 2.7 cmH2O
for the new nasogastric polyfunctional catheter and
standard balloon catheter, respectively. The regression
equation calculated according to the Passing and Bablok
method, considering the IGPEEO between the two meth-
ods, had an intercept of -0.1493 (95% CI -3.0595 to
1.7500) and a slope of 0.9841 (95% CI 0.7500–1.2619).
The Bland–Altman analysis showed a bias of -0.45
(-2.85 to 1.95) cmH2O (Fig. 2c). The CCC was 0.89
(95% CI 0.75–0.95); this value translates into a within-
sample variability of about 33% of the total variability.
The new nasogastric polyfunctional catheter was
successfully inserted in all the subjects, and it was left in
some patients after the study depending on their clinical
requirements. No side effects or complications were
recorded.
Discussion
The primary finding of this study is that the new naso-
gastric polyfunctional catheter is able to record both the
esophageal and intragastric pressure similarly to a stan-
dard balloon catheter.
The respiratory system includes the lung and the chest
wall, and consequently the mechanical behavior depends
on the mechanical properties of these two components
[4]. The distending force of the lung is not the airway
pressure, which is commonly used in clinical practice, but
the transpulmonary pressure [8].
The measurement of esophageal pressure, obtained by
an esophageal balloon, has been used as an estimate of
pleural pressure since Buytendijk [18] pioneered the
technique. The most widely used method employs an air-
containing balloon sealed over a catheter, which transmits
balloon pressure to manometers or, more recently, to
monitoring transducers [10, 11]. When simultaneously
recorded in spontaneous breathing subjects, the esopha-
geal pressure changed at the same rate as the pleural
pressure, but it was consistently more positive [18, 19]. In
an experimental study, the esophageal pressure only
reflected the pleural pressure measured in the middle
regions, whereas it overestimated the pleural pressure in
the non-dependent lung regions and underestimated it in
the dependent lung regions [20].
In the present study the new nasogastric polyfunc-
tional catheter showed a good clinical agreement
compared to a standard balloon catheter in estimating
either the absolute or the changes of esophageal pressure
in mechanically ventilated patients. The level of agree-
ment was slightly lower when recording the absolute
esophageal pressure compared with the variations of
esophageal pressure during the tidal inflation. This was
probably due to the difference in location of the balloon
of the new nasogastric polyfunctional catheter in the
esophagus compared with the standard balloon catheter.
To minimize the pressure artifacts due to the catheter
itself, we employed a balloon 10-cm long with a very thin
wall, inflated with a minimum amount of air volume, to
not increase the pressure inside the balloon, and posi-
tioned in the lower part of the esophagus [9–11].
Several techniques have been proposed for the mea-
surement of intra-abdominal pressure [12]. The bladder
technique was originally described by Kron et al. [21] in
which the bladder was infused with 50–100 ml of saline
via the patients’ Foley catheter and the pressure was
recorded by a pressure transducer at the symphysis pubis.
The bladder technique, due to its simplicity, low cost, and
excellent correlation with direct measurement of intra-
abdominal pressure, still remains the most common
technique. However, it is time consuming, it requires
instillation of saline into the bladder, it is intermittent and,
moreover, gives a trend of intra-abdominal pressure
depending on the interval between separate measurements
[12]. Previous studies showed that the intra-abdominal
pressure can be also accurately measured by the intra-
gastric pressure [22]. In our experimental setting, the bias
in recording the intragastric pressure was clinically
acceptable. Even though the width of the agreement bands
may be considered numerically high, the agreement was
judged to be acceptable because the variations of a few
units are not relevant.
Thus, the intragastric pressure can be considered an
alternative in patients without bladder catheter, in cases of
bladder trauma, pelvic hematomas or fractures, and in all
the clinical situations in which a continuous monitoring of
intra-abdominal pressure is advisable.
Conclusions
Because the majority of patients admitted to ICU require
a nasogastric catheter for nutrition during mechanical
ventilation, the new nasogastric polyfunctional catheter
can be a good alternative allowing the possibility to
continuously monitor esophageal and intragastric pres-
sure. The knowledge of esophageal and intragastric
pressures should help in tailoring a more ‘‘physiologic’’
mechanical ventilation.
a
mean of PesEEO new nasogastric polyfunctional catheter and
PesEEO standard balloon catheter (cmH2O)
Difference between Pes
EEO
new nasogastric poly
functional catheter
and Pes
EEO
standard balloo
n catheter (cmH
2O)
-4
-2
0
2
4
b
mean of deltaPes new nasogastric polyfunctional catheter and
deltaPes standard balloon catheter (cmH2O)
6
8
10
12
14
16
18
20
22
0
1
2
3
4
5
6
7
8
Difference between deltaPes new naso
gastric polyfunctional catheter
and deltaPes
standard balloon catheter (cmH
2O)
-2
-1
0
1
2
c
mean of IGPEEO new nasogastric polyfunctional catheter and
IGPEEO standard balloon catheter (cmH2O)
4
6
8
10
12
14
16
18
Difference between IGP
EEO
new nasogastric polyfunctional catheter
and IGP
EEO
standard balloon catheter (cmH
2O)
-4
-2
0
2
4
Fig. 2 a Bland–Altman analysis of the esophageal pressure
measured with the new nasogastric polyfunctional catheter and
the standard balloon catheter. The x-axis shows the mean of the two
measurements and the y-axis the difference between the esophageal
pressure measured with the new nasogastric polyfunctional catheter
and the standard balloon catheter. b Bland–Altman analysis of the
delta esophageal pressure measured with the new nasogastric
polyfunctional catheter and the standard balloon catheter. The
x-axis shows the mean of the two measurements and the y-axis the
difference between the delta esophageal pressure measured with
the new nasogastric polyfunctional catheter and the standard
balloon catheter. c Bland–Altman analysis of the intragastric
pressure measured with the new nasogastric polyfunctional catheter
and the standard balloon catheter. The x-axis shows the mean of the
two measurements and the y-axis the difference between the
intragastric pressure measured with the new nasogastric polyfunc-
tional catheter and the standard balloon catheter
b
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